Manufacture of corrugated metal tubes or bellows



J. H. MlLLAR 3,375,689

MANUFACTURE OF CORRUGATED METAL TUBES OR BELLOWS A ril 2, 1968 3 Sheets-Sheet 1 Filed Sept. 10, 1964 {M MWWQL J. H. MILLAR April 2, 1968 MANUFACTURE OF CORRUGATED METAL TUBES OR BELLOWS Filed Sept. 10, 1964 5 Sheets-Sheet 2 lnveril'or M0 WW April 1968 I J. H. MILLAR 3,375,689

MANUFACTURE OF CORRUGATED METAL TUBES OR BELLOWS Filed Sept. 10, 1964 5 Sheets-Sheet 5 5L v T m 4&5 I N6. K /fi by -20 4 I A I T 6 45 4 flza 24 I In mor *4 We,

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United States Patent MANUFACTURE OF CORRUGATED METAL TUBES 0R BELLOWS John Humphrey Millar, 6 Chelsea Lodge, Tite St., London SW. 3, England Filed Sept. 10, 1964, Ser. No. 395,525 Claims priority, application Great Britain, Sept. 12, 1963, 36,032/63 2 Claims. (Cl. 72-59) This invention relates to a process and machinery for the forming of thin walled metal tubing into corrugated tubing or bellows the surface of which is formed with a series of annular convolutions or corrugations.

The corrugations of such tubes have to be regular and it is preferable that the sides of each corrugation be substantially parallel to each other and perpendicular to the longitudinal axes of the tube. This is difficult to achieve as there is a tendency for the corrugations to open out or spring back after forming and to then assume a roughly triangular shape which is most undesirable.

A process for corrugating tubing in accordance with the invention comprises surrounding the portion of the tube on which a corrugation is to be formed with a two-part die or the like having an internal groove or recess the sides of which have the shape of a corrugation but which are not necessarily fully closed, expanding the tube wall into the recess in the die by means of internally applied pressure partially to form a corrugation in the tube wall, closing up one part of the die longitudinally and then releasing the internal pressure somewhat, withdrawing one part of the die longitudinally and then forcibly reclosing or kicking the said one die-part against the other to set the corrugation to its final shape without spring back.

It has been found that when the die is opened initially the corrugation just formed spreads open or springs back somewhat and that the kicking-up of the movable die part with reduced pressure within the corrugation, squeezes the corrugation and probably especially the crest thereof so that its final form assumes the shape of the die cavity or recess without noticeable spring back.

Preferably an initial forming step is performed in which the two parts of the die are held only partially closed and the internal pressure is employed partially to form a corrugation, the two parts of the die being then completely closed and the complete corrugation formed.

The internal pressure may be provided by means of a rubber block which is compressed longitudinally so that it tends to spread out transversely and thus cause the wall of the tube to flow into the die cavity or groove or the internal pressure may be applied by using hydraulic fluid.

A machine in accordance with the invention for carrying out the process set out above comprises a two part die which is arranged to surround a tube being corrugated, means to move one part of the die relatively to the other in the longitudinal direction of the tube and means to apply internal pressure to that portion of the tube held within the ring die.

The movable die part is preferably in the shape of a cylinder surrounding the tube with its end face directed towards the other part of the die and formed with a groove having the shape of a portion of the corrugation, the other die part having its corresponding end face formed with the other portion of the corrugation. This die part preferably also has a complete corrugation groove formed in it adjacent its end to receive and hold the adjacent previously formed corrugation while the next corrugation is being formed.

This .part of the die is preferably formed in two halves which are in fact movable in a direction transverse to the 'ice longitudinal axis of the machine. The tube can thus be moved through the machine by opening the two parts of the fixed die after the corrugation has been formed, indexing the parts back by the pitch length of one corrugation, re-closing the two parts around the tube so that the just formed corrugation is engaged in the complete corrugation groove formed in the die and then moving the die forward again by the distance of one corrugation pitch so that the tube is moved forward by this distance and so that the un formed portion of the tube adjacent the previously formed corrugation is positioned ready for the formation of a further corrugation.

An example of a machine in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic perspective view of the machine;

FIGURE 2 is a section of the means for applying internal pressure to the tube being formed; and

FIGURES 3, 4, and 5 are diagrams illustrating the various stages of the formation of a corrugation in the tube.

The machine comprises essentially a mandrel 2 on which a tube 4 which is being corrugated by the machine slides, and a two part die comprising a relatively fixed part generally indicated at 6, and a cylindrical die 8. The die 6 is formed in two halves 10 and .12 each formed internally with one half of a complete annular groove 14 having the shape of one corrugation of the tube, and, on their mating inner end faces with a half groove 16 rep-resenting one half of a corrugation. The two halves 10 and 12 of the die are movable into and out from engagement with the tube by means of hydraulic motors 18 in a direction perpendicular to that of the axis of the tube. The cylindrical die 8 which surrounds the unformed portion of the tube is provided in its end face facing the die part 6, with a groove 20 representing one half of a corrugation. This cylindrical die is movable in a direction parallel to the axis of the tube 4 by means of a hydraulic motor 22 the piston 24 of which acts on the upper end of a lever 26 the lower end of which is fixed to the cylindrical die and which is pivoted, between its ends, at 28.

The die 6 and servo-motors 18 are mounted on a platform 30 which is slidable in a direction parallel to the tube axis and which is moved by means of a hydraulic motor 32 acting though a line 34 and a toggle device (not shown).

When a corrugation is to be formed in the tube the two parts 10, 12 of the die 6 are closed around the tube and the cylindrical die 8 is moved towards the die 6 leaving a slight gap therebetween as can be seen in FIGURE 2. Internal pressure is then applied to the tube wall by means of a rubber block 36 which is compressed between the end of the mandrel 2 and a metal block 38- by movement of the block 38 axially towards the end of the mandrel 2 which movement is caused by a motor 40 through a piston 42 extending within the mandrel 2 and the outer end of which is secured to the metal block 38.

The initial compression of the rubber block 36 is such as to partially force the tube wall into the gap 44 between the cylindrical die and the die 6 as can be seen in FIG- URE 2. The cylindrical die is then moved axially towards the die 6 so that the faces of the two dies abut leaving the groove 44 formed by the portions 16-20 of the dies 6 and 8 respectively with the width of a corrugation. The rubber block is then further compressed so as to force the portion of the tube completely into the groove as can be seen in FIGURE 3 and so as to form a complete corrugation 46.

The compressive force applied to the rubber block 36 is reduced, then the cylindrical die 8 is withdrawn axially away from the die 6 as can be seen in FIGURE 4 Whereupon the just formed corrugation 46 springs-bat: or relaxes somewhat as can also be seen in FIGURE 4. The cylindrical die is then sharply kicked-up or bangedup against the die 6 so as to reassure the position shown in FIGURE 3 but with the rubber block extending only about half Way up the corrugation. This kicking-up movement has the effect of setting the corrugation 46 and it has been found that when the cylindrical die is again opened out from the die 6, the corrugation remains in its desired shape with the sides parallel and perpendicular to the axis of the tube.

The tube is then indexed forwardly ready for the formation of the next corrugation. This is done by opening out the two halves 10 and 12 of the die 6 to the position shown in FIGURE 1 by means of the motors 18, and then moving the platform 30 to the left as seen in FIGURE 1 by a distance equal to the distance between the successive corrugation crests so that the groove 14 in the die 6 is positioned opposite to the just formed corrugation 46. The two halves of the die 6 are then moved perpendicularly inwardly so that the corrugation is trapped in the groove 14 and the platform 30 is moved to the right as seen in FIGURE 1 through the distance of one corrugation so that the parts are positioned ready for the formation of the next corrugation as seen in FIGURE 5. The fact that the just formed corrugation 46 is securely held in the die 6 helps accurately to position the tube for the formation of the next successive co rrugation and firmly to hold the tube during the formation of this corrugation.

Instead of having two motors 18 to move the two halves of the die 6 a single motor may be provided positioned for example beneath the mandrel 2 and acting on the two halves of the die 6 through a toggle linkage so that the two halves are moved simultaneously an equal distance and with equal pressure.

Furthermore the cylindrical die motor 22 may be positioned beneath the level of the mandrel and act on the die 8 through a short lever terminating in a fork. This modification leads to a more compact design and possibly the application of larger forces.

Conveniently two adjustable stops (not shown in the drawings) are provided on the drive for the piston 42 corresponding to the positions of full and partial compression of the block 36 so the full force can be applied at each stage.

The machine is especially useful for tubes having a wall thickness of from 0.002 inch to 0.02 inch and in which the depth of corrugation or convolution is up to 25% of the outside radius of the tube or bellows after corrugation.

I claim:

1. A process for corrugating tubing comprising surrounding the portion of the tube on which a corrugation is to be formed with a two-part die having an internal groove or recess having a width of a corrugation on the parting line of the die, closing the die parts and expanding the tube wall into the recess to completely fill the recess in the die by means of internally applied pressure to form a complete corrugation in the tube wall and then releasing the internal pressure somewhat, Withdrawing one part of the die longitudinally to permit the corruga tion to partly spring back and then forcibly re-closing or kicking the said one die part against the other with the initially internally applied pressure partly reduced to set the corrugation to its final shape.

2. A process as claimed in claim 1 in which an initial forming step is carried out in which the two parts of the die are only partially closed and internal pressure is applied partially to form a corrugation the two faces of the die being then completely closed and the complete corrugation formed.

References Cited UNITED STATES PATENTS 2,581,787 1/1952 Dreyer 72-59 2,773,538 12/1956 DeMers 72 59 2,825,387 3/1958 Alltop 72-59 CHARLES W. LANI-IAM, Primary Examiner.

K. C. DECKER, Assistant Examiner. 

1. A PROCESS FOR CORRUGATING TUBING COMPRISING SURROUNDING THE PORTION OF THE TUBE ON WHICH A CORRUGATION IS TO BE FORMED WITH A TWO-PART DIE HAVING AN INTERNAL GROOVE OR RECESS HAVING A WIDTH OF A CORRUGATION ON THE PARTING LINE OF THE DIE, CLOSING THE DIE PARTS AND EXPANDING THE TUBE WALL INTO THE RECESS TO COMPLETELY FILL THE RECESS IN THE DIE BY MEANS OF INTERNALLY APPLIED PRESSURE TO FORM A COMPLETE CORRUGATION IN THE TUBE WALL AND THEN RELEASING THE INTERNAL PRESSURE SOMEWHAT, WITHDRAWING ONE PART OF THE DIE LONGITUDINALLY TO PERMIT THE CORRUGATION TO PARTLY SPRING BACK AND THEN FORCIBLY RE-CLOSING OR "KICKING" THE SAID ONE DIE PART AGAINST THE OTHER WITH THE INITIALLY INTERNALLY APPLIED PRESSURE PARTLY REDUCED TO SET THE CORRUGATION TO ITS FINAL SHAPE. 